It is well known that the use of diamond coatings offers many advantages in several fields of use. Diamond coated saws and drills are used to cut concrete and steel. Drill bits coated with a thin layer of diamond may be used at much higher rotational velocities with much greater efficiency than standard drill bits. In the field of surgery, some procedures require ultra-sharp scalpels coated with a thin diamond film.
It is well known that the advantages given by diamond coated tools are due mainly to the physical characteristics of the diamond. Namely, diamonds exhibit low expansion when heated and have a high degree of hardness and heat conductivity. Diamond also has a low coefficient of friction.
The deposition of thin diamond coatings has been taught by others. Typically, thin films are only a few Angstroms to 1 micron thick. Typical of the art are those devices disclosed in the following patents:
______________________________________ Patent No. Inventor Date ______________________________________ US 4,767,608 Matsumoto et al. Aug. 30, 1988 US 4,842,937 Meyer, et al. June 27, 1989 US 4,988,421 Drawl, et al. Jan. 29, 1991 US 4,992,082 Drawl, et al. Feb. 12, 1991 US 5,174,983 Snail Dec. 29, 1992 US 5,260,106 Kawarada et al. Nov. 9, 1993 EP 0,470,644 Bigelow Feb. 12, 1992 JP 3,141,193 Kurihara Oct. 24, 1989 JP 88,707 Apr. 15, 1991 JP 117,993 May 21, 1988 JP 164,795 June 25, 1989 ______________________________________
The Meyer patent ('937) discloses multilayer deposition on the surface of a cutting tool, the layers varying in composition from the first layer to the last. The Meyer patent does not disclose the deposition of a single thick layer of a diamond or diamond-like material on a selected substrate.
The Drawl patents ('421 and '082), the latter being a divisional of the former, describe a process of toughening diamond or diamond-like coatings through the use of chemical vapor deposition (CVD). In the Drawl process, a plurality of layers of diamond or diamond-like particles is deposited with a layer of mechanically adherent, planarized binding material being interposed between each respective pair of diamond or diamond-like layers.
Kurihara discloses a method of manufacturing a diamond film by applying a coat of thick film paste composed of diamond particles and metallic powder. The thick film is then baked in an inactive gas atmosphere to form a middle layer of diamond particles and metal. This middle layer is then polished. The substrate is then mounted in a DC plasma gas phase growth device and subjected to hydrogen gas containing carbon gas to attain gas phase growth of the diamond.
Each of the Drawl patents and the Kurihara application disclose the use of CVD, which requires the use of a chamber in which the diamond growth occurs. In some applications of diamond coatings, it may be desirable to be able to produce the diamond film in the field where facilities for CVD are unavailable. Such a method may include a DC arc plasma. Though Kurihara employs a DC plasma, it is used there in conjunction with a CVD device.
The European patent ('644) issued to Bigelow uses DC arc assisted plasma deposition to form a multi-layer film, each layer being fabricated from similar chemical compositions. The individual layers of diamond may be separated by a thin layer of graphite.
It is well known that each layer adds to the complexity of the manufacture of the film. Therefore, it is desirable to manufacture a thick film of diamond or diamond-like material on a selected substrate wherein the thick film consists of a single layer.
The Matsumoto et al, Snail and Kawarada et al references are all directed to a vapor-phase system, and thus to a type of CVD process. This is also true of the '993 and '759 Japanese patent references. The '707 Japanese patent reference teaches the formation of diamond particles by irradiating glassy carbon that was deposited on a surface, the diamond particles being scattered from that surface. Further, there is a teaching that the process occurs at a relatively low pressure--in contrast to atmospheric pressure.
Therefore, it is an object of this invention to provide a means for depositing a single thick layer of diamond or a diamond-like film over a selected portion of a selected substrate.
It is also an object of the present invention to provide a means whereby a thick diamond film may be deposited in a selected environment not requiring the use of a deposition chamber and, therefore, the coating can be applied at normal atmosphere pressure.
Still another object of the present invention is to provide a means for depositing a thick diamond or diamond-like film using a DC plasma torch wherein powders are heated to at lease a softened state in an inert atmosphere and propelled against a substrate where the diamond coating is produced by transformation when the heated powder is quenched.